Updated

The U.N. is keeping its peacekeeping force in Congo for another year as the country looks anxiously ahead to a long-delayed presidential election.

The Security Council voted unanimously Tuesday to extend its biggest and costliest peacekeeping effort.

The force recently endured the deadliest single assault on a U.N. peacekeeping force in almost 25 years. A rebel attack late last year killed 15 troops.

Congo has gone through decades of ethnic clashes, rebellions and violence carried out by armed groups and militias trying to control gold and other resources.

Tensions also have simmered over President Joseph Kabila's stay in office. His mandate ended in 2016, but elections have repeatedly been postponed. They are now set for Dec. 23.

The $1.1 billion-a-year peacekeeping mission counts over 16,000 troops and 1,300 police.